The present invention relates to an equalization apparatus and method for controlling the charging of a battery pack comprising a plurality of series-connected batteries. More particularly, it concerns an equalization circuit adapted for use during a constant current charging phase of a battery pack associated with a two-wheeled electrical motor scooter.
The prior art teaches a number of methods for charging a battery pack comprising a plurality of series-connected batteries. A well-known approach is to first charge them at a constant voltage until they are partially charged and further charging them at a constant current to bring them to a full charge. Another technique, taught in U.S. Pat. No. 5,637,979 to Tamai et al,. is to charge them at a constant current until any one battery reaches a predetermined voltage, and then reduce the charging current to that battery, while increasing the voltage applied to the remaining batteries.
Regardless of the approach taken to charge the battery pack, equalization must be performed to ensure that batteries are evenly charged. Uneven charging among the batteries in a battery pack degrades its ability to supply sufficient power to a given load, and also shortens the life of the batteries in the battery pack. Typically, during a constant current charging phase, an equalization circuit gauges the charge status of each battery, and diverts and allocates charging current, as needed, among the batteries in the battery pack.
Most often, the charge state of a battery is determined by measuring its voltage and temperature, and perhaps also other parameters. The equalization circuit then prevents overcharging by bypassing current once the batteries have become fully charged, as determined by one or more voltage and current saturation detecting mechanisms. In this regard, U.S. Pat. No. 5,504,415 to Podrazhansky is directed to an equalization circuit which takes into consideration individual battery temperature to perform equalization, and shunts current around batteries based on their temperatures. U.S. Pat. No. 5,592,067 to Peter et al. employs switched mode power converters to regulate equalization cell circuits associated with each pair of adjacent batteries, based on a comparison of voltages of those batteries. U.S. Pat. No. 5,578,914 to Morita discloses circuitry for constant voltage charging and subsequent detection of saturation of a bypass current to prevent damage to the batteries. The contents of the above patents are incorporated by reference to the extent necessary to understand the present invention.